Effects of Soil pH on the Growth and Cadmium Accumulation in Polygonum hydropiper (L.) in Low and Moderately Cadmium-Contaminated Paddy Soil

Abstract

Wetland macrophytes have advantages when used in the remediation of cadmium (Cd)-contaminated paddy fields because they can adapt to overly wet soil environments; however, only a few studies have tested the efficiency of macrophytes in Cd phytoremediation. In this study, we investigated the effect of soil pH (pHs of 5, 6, and 7) on the accumulation and translocation of Cd by Polygonum hydropiper (L.) in low and moderately Cd-contaminated paddy soil (0.56 and 0.92 mg/kg, respectively). Our results indicated that Cd accumulation in stems and roots, as well as subcellular distribution in P. hydropiper, was affected by soil pH, with significant interactions between the soil pH and Cd level. At low soil Cd levels, stem and root Cd contents were higher at a soil pH value of 6. In addition, with higher soil pH values, the proportion of Cd distributed in the cell wall increased, whereas that distributed in the organelles decreased. The Cd content in the roots and stems of P. hydropiper significantly decreased with the increase in soil pH in the moderate Cd-contaminated soil. In addition, with higher soil pH values, the proportion of Cd distributed in the cell wall decreased, whereas that distributed in the organelles increased. The translocation factor (TF) of P. hydropiper was higher than one in all treatments, indicating that it can effectively transport root-absorbed Cd to the aboveground shoots. Based on the relatively high bioconcentration factor and TF, P. hydropiper has the potential to remediate Cd-polluted paddy soil. Furthermore, the remediation efficiency of P. hydropiper can be enhanced by adjusting the pH as per the soil-Cd pollution.